1. Field of the Invention
The present invention relates generally to medical devices and methods. More particularly, the present invention relates to the use of an expandable scoring cage for disrupting stenotic deposits in cardiac valves.
Stenosis of the aortic and other cardiac valves occurs when the valve annulus narrows restricting the flow of blood through the valve when open. This is a particular problem with aortic valve stenosis where the flow of oxygenated blood from the left ventricle to the rest of the body is limited. When the aortic valve is obstructed, the heart must pump at a higher pressure to overcome the increased resistance which can weaken the heart and lead to various symptoms, such as fatigue, chest pain, heart palpitation, heart murmur, and ultimately heart failure. The traditional treatment for aortic valve stenosis has been heart valve replacement through open chest, stopped heart procedures. Recently, percutaneous heart valve replacement has become available. For many patients, however, heart valve replacement is not a realistic choice. Some patients are too weak or ill to undergo such procedures. Other patients are at the beginning stages of valve stenosis where performing a valve replacement procedure might not be justified.
For such patients, it would be desirable to provide alternative therapeutic procedures. Valve angioplasty is one such alternative procedure. A balloon catheter is introduced to the aortic valve, typically through an aortic arch approach, and the balloon inflated within the heart valve to disrupt and loosen stenotic material located on the valve leaflets and in the valve annulus. While such procedures have been clinically employed, they suffer from a number of shortcomings. The principal shortcoming is a lack of effectiveness in some patients. The radial pressure applied by the balloons is not always directed symmetrically, and the balloons can often slip from their original placement within the valve annulus. Both these circumstances limit the effectiveness of conventional valvuloplasty therapy. Moreover, the valvuloplasty balloons must be very large (in order to accommodate the valve annulus), thus requiring a relatively long deflation period. Since the aorta can only be blocked for a short period of time, the need to provide for a lengthy deflation time limits the treatment time in which the balloon can be fully inflated. Additionally, the deflation of such large balloons often leaves a very uneven profile with flaps and portions of the balloon extending radially outwardly. The removal of such structures from the valve annulus can damage the fragile valve leaflets as well as the vasculature through which the catheter is removed. Additionally, valvuloplasty has generally been limited to the treatment of aortic valves.
For these reasons, it would be desirable to provide improved apparatus and methods for performing cardiac valve angioplasty. It would be particularly useful if the methods and apparatus provided for more effective treatment of cardiac valve stenoses, not only in the aorta but in other cardiac valves as well, such as the mitral valve and the pulmonary valve. It would be further desirable to provide valvuloplasty balloons which are capable of applying force symmetrically about their perimeter in order to more effectively treat and fracture stenotic material surrounding the valve annulus. It would be still further desirable if the valvuloplasty balloons were able to resist slippage while inflated, thus improving effectiveness and reducing the risk of left ventricular perforations. It would be still further useful if the valvuloplasty balloons were adapted for rapid deflation so that the period of inflation intended to treat the valve could be prolonged. Additionally, it would be useful if the valvuloplasty balloons folded in a regular manner with a low profile to facilitate removal of the balloons and reduce the risk of trauma to the valve leaflets or other harder vascular structures. At least some of these objectives will be met by the invention as described herein below.
2. Description of the Background Art
Catheters for treating cardiac valve stenoses are described in the following U.S. Patents and Published Applications: U.S. Pat. Nos. 4,986,830; 5,443,446; 6,746,463; 7,029,483; 7,455,652; US 2005/0137690; and 2006/0074484. Commonly owned patents and pending applications which relate to the invention herein include: U.S. Pat. Nos. 7,686,824; 7,691;119; 2004/0243158; 2005/0021071; 2005/0021070; 2006/0259005; 2006/0085025; 2009/0105687; and 2010/0121372, the full disclosures of which are incorporated herein by reference.